Melaleuca Alternifolia Tea Tree oil (TTO) is an essential oil steam-distilled from a plant that originates in Australia, Melaleuca alternifolia belonging to the Myrtaceae family.

It appears as a yellowish oily liquid.

It has been shown to be non-toxic, non-irritating and non-corrosive to humans only at the doses set by medical warnings (1).

Human health

TTO exhibits a wide spectrum of anti-bacterial, anti-viral, and anti-inflammatory activities. Its wide range of antimicrobial activity is mainly due to its diversity of components, especially its volatile constituents. The volatile compounds in TTO are mainly 1,8-cineole, terpinen-4-ol, and α-terpilenol (2).

In particular, 1,8-cineole has been shown to destroy the cell menbrane of E. coli, while terpinen-4-ol exhibits strong antibacterial, disinfection, and anti-corrosive effects. α-terpilenol has been demonstrated to feature suitable permeability and exhibits a killing effect on common pathogens such as Staphylococcus aureus, E. coli, pseudomonas aeruginosa, candida aibicans, etc.(3).

TTO is not harmful to the human body and has a suitable, natural anti-bacterial effect; thus, it may be used as an anti-bacterial agent in food.
Several studies have suggested the uses of TTO for the treatment of acne vulgaris, seborrheic dermatitis, and chronic gingivitis. It also accelerates the wound healing process and exhibits anti‐skin cancer activity (4).

Agriculture

Botrytis cinerea, one of the most destructive fungal pathogens, causing gray mold rot in a wide range of fresh fruits and vegetables. Although chemical fungicides are widely used to control the incidence of the disease, this practice potentially introduces harmful substances into the food chain, and also selects for B. cinerea strains with increased drug resistance. This study found that important metabolic pathways, including glycolysis, the TCA cycle, and purine metabolism, were compromised by TTO treatment, while Cytochrome c (a hemoglobin located in the inner mitochondrial membrane, and is responsible for transferring electrons between mitochondrial electron transport chain complexes) increased. We conclude that the disruption of energy metabolism by TTO contributes to its antifungal activity against B. cinerea (5).

The most relevant studies on this ingredient have been selected with a summary of their contents:

Melaleuca Alternifolia studies

CTypical commercial product characteristics Melaleuca Alternifolia Tea tree oil

• Molecular Formula      C₂₈H₆₀O₄P₂S₄Zn
• Molecular Weight 716.352 g/mol
• CAS:   68647-73-4
• EC Number: 232-293-8     
• UNII     VIF565UC2G
• DSSTox Substance ID  DTXSID6028789      DTXSID60100611      DTXSID30874014
• IUPAC  zinc;diheptoxy-sulfanylidene-sulfido-λ⁵-phosphane
• InChl=1S/2C14H31O2PS2.Zn/c2*1-3-5-7-9-11-13-15-17(18,19)16-14-12-10-8-6-4-2;/h2*3-14H2,1-2H3,(H,18,19);/q;;+2/p-2
• InChl Key      ZKAQFYDDTYGBBV-UHFFFAOYSA-L
• SMILES  CCCCCCCOP(=S)(OCCCCCCC)[S-].CCCCCCCOP(=S)(OCCCCCCC)[S-].[Zn+2]
• MDL number  MFCD00132409
• PubChem Substance ID    
• RTECS  RJ3697600
• NCI    C74295
• C74295     69627 
• FEMA Number: 3902

Synonyms:

• Melaleuca alternifolia Oil
• Phosphorodithioic acid, O,O-di-C1-14-alkyl esters, zinc salts
• Oil, Melaleuca alternifolia
• TEA TREE OIL
• Oil, Tea Tree
• Tea Tree Oil
• Dialkyl(C1-C14)dithiophosphoric acid, zinc salt
• SCHEMBL164653
• zinc diheptoxy-sulfido-thioxo-$l^{5}-phosphane
• Zinc Dialkylphosphorodithiloate
• AN-38072

References__________________________________________________________________

(1) Hammer KA, Carson CF, Riley TV. In vitro activity of Melaleuca alternifolia (tea tree) oil against dermatophytes and other filamentous fungi. J Antimicrob Chemother. 2002 Aug;50(2):195-9. doi: 10.1093/jac/dkf112.

Abstract. The in vitro activity of Melaleuca alternifolia (tea tree) oil against dermatophytes (n = 106) and filamentous fungi (n = 78) was determined. Tea tree oil MICs for all fungi ranged from 0.004% to 0.25% and minimum fungicidal concentrations (MFCs) ranged from <0.03% to 8.0%. Time-kill experiments with 1-4 x MFC demonstrated that three of the four test organisms were still detected after 8 h of treatment, but not after 24 h. Comparison of the susceptibility to tea tree oil of germinated and non-germinated Aspergillus niger conidia showed germinated conidia to be more susceptible than non-germinated conidia. These data demonstrate that tea tree oil has both inhibitory and fungicidal activity.

(2) Lin G, Chen H, Zhou H, Zhou X, Xu H. Preparation of Tea Tree Oil/Poly(styrene-butyl methacrylate) Microspheres with Sustained Release and Anti-Bacterial Properties. Materials (Basel). 2018 May 1;11(5):710. doi: 10.3390/ma11050710.

Abstract. Using butyl methacrylate (BMA) and styrene (St) as monomers and divinylbenzene (DVB) as a crosslinking agent, P(St-BMA) microspheres were prepared by suspension polymerization. Tea tree oil (TTO) microspheres were prepared by adsorbing TTO on P(St-BMA) microspheres. The structure and surface morphology of P(St-BMA) microspheres and TTO microspheres were characterized by Fourier transformed infrared spectroscopy (FTIR), optical microscopy, and Thermogravimetric analysis (TGA). In doing so, the structural effect of P(St-BMA) microspheres on oil absorption and sustained release properties could be investigated. The results show that the surface of the P(St-BMA) microspheres in the process of TTO microsphere formation changed from initially concave to convex. The TTO microspheres significantly improved the stability of TTO, which was found to completely decompose as the temperature of the TTO increased from about 110 &deg;C to 150 &deg;C. The oil absorption behavior, which was up to 3.85 g/g, could be controlled by adjusting the monomer ratio and the amount of crosslinking agent. Based on Fickian diffusion, the sustained release behavior of TTO microspheres was consistent with the Korsmeyer-Pappas kinetic model. After 13 h of natural release, the anti-bacterial effect of the TTO microspheres was found to be significantly improved compared to TTO.

(3) Thomas J, Carson CF, Peterson GM, Walton SF, Hammer KA, Naunton M, Davey RC, Spelman T, Dettwiller P, Kyle G, Cooper GM, Baby KE. Therapeutic Potential of Tea Tree Oil for Scabies. Am J Trop Med Hyg. 2016 Feb;94(2):258-266. doi: 10.4269/ajtmh.14-0515. 

(4)  Pazyar N, Yaghoobi R, Bagherani N, Kazerouni A. A review of applications of tea tree oil in dermatology. Int J Dermatol. 2013 Jul;52(7):784-90. doi: 10.1111/j.1365-4632.2012.05654.x.

(5) Xu J, Shao X, Wei Y, Xu F, Wang H. iTRAQ Proteomic Analysis Reveals That Metabolic Pathways Involving Energy Metabolism Are Affected by Tea Tree Oil in Botrytis cinerea. Front Microbiol. 2017 Oct 12;8:1989. doi: 10.3389/fmicb.2017.01989.

Abstract. Tea tree oil (TTO) is a volatile essential oil obtained from the leaves of the Australian tree Melaleuca alternifolia by vapor distillation. Previously, we demonstrated that TTO has a strong inhibitory effect on Botrytis cinerea. This study investigates the underlying antifungal mechanisms at the molecular level. A proteomics approach using isobaric tags for relative and absolute quantification (iTRAQ) was adopted to investigate the effects of TTO on B. cinerea. A total of 718 differentially expression proteins (DEPs) were identified in TTO-treated samples, 17 were markedly up-regulated and 701 were significantly down-regulated. Among the 718 DEPs, 562 were annotated and classified into 30 functional groups by GO (gene ontology) analysis. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis linked 562 DEPs to 133 different biochemical pathways, involving glycolysis, the tricarboxylic acid cycle (TCA cycle), and purine metabolism. Additional experiments indicated that TTO destroys cell membranes and decreases the activities of three enzymes related to the TCA cycle. Our results suggest that TTO treatment inhibits glycolysis, disrupts the TCA cycle, and induces mitochondrial dysfunction, thereby disrupting energy metabolism. This study provides new insights into the mechanisms underlying the antifungal activity of essential oils.